1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
#include<bits/stdc++.h>

using namespace std;

int MOD = 1e9 + 7;

class Node{
	public:
	int left = -1;
	int right = -1;
	int l;
	int r;
	int val;

};

class Tree{
private:
	vector<Node> v;
	int l, r;
	
	int createNode(int L, int R){
		Node node;
		node.l = L;
		node.r = R;
		node.val = 0;
		v.push_back(node);
		//cout<<"Created "<<v.size()<<"\n";
		return (v.size() -1);
	}
	
	void addNumber(int pos, int current, int number){
		//cout<<v[current].l<<" "<<v[current].r<<"\n";
		if(v[current].l == v[current].r){
			v[current].val = (v[current].val + number) % MOD;
		}else{
			int m = (v[current].l + v[current].r) / 2;
			if(v[current].left == -1){
				int x = createNode(v[current].l, m);
				v[current].left = x;
			}
			if(v[current].right == -1){
				int x = createNode(m+1, v[current].r);
				v[current].right = x;
			}
			if(pos <= m){
				addNumber(pos, v[current].left, number);
			}else{
				addNumber(pos, v[current].right, number);
			}
			v[current].val = (v[v[current].left].val + v[v[current].right].val) % MOD;
		}
	}
	
	int rangeSum(int a, int b, int current){
		if(a <= v[current].l && v[current].r <= b){
			return v[current].val;
		}else if(a > v[current].r || b < v[current].l){
			return 0;
		}else{
			int m = (v[current].l + v[current].r) / 2;
			if(v[current].left == -1){
				int x = createNode(v[current].l, m);
				v[current].left = x;
			}
			if(v[current].right == -1){
				int x = createNode(m+1, v[current].r);
				v[current].right = x;
			}
			return (rangeSum(a, b, v[current].left) + rangeSum(a, b, v[current].right))% MOD;
		}
	}
	
public:
	
	Tree(int size){
		l = 0;
		int k = 1;
		while(k < size)k*= 2;
		r = k-1;
		Node node;
		node.l = l;
		node.r = r;
		node.val = 0;
		v.push_back(node);
	}
	
	void add(int pos, int val){
		addNumber(pos, 0, val);
	}
		
	int getSum(int a, int b){
		return rangeSum(a, b, 0);
	}	
};

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	srand(time(NULL));
	int n; cin>>n;
	vector<int> v(n, 0); for(int i = 0; i < n; i++)cin>>v[i];
	Tree odd(MOD);
	Tree even(MOD);
	even.add(0, 1);
	int shift = 0;
	long long res = 0;
	for(int i = 0; i < n; i++){
		int a = v[i];
		int good = 0;
		int a1 = (a - shift) % 2;
		if(a1 < 0)a1 += 2;
		if(a1 == 0){
			good += even.getSum(0, MOD - a - 1 - shift);
			good %= MOD;
			good += even.getSum(MOD - shift, MOD - 1);
			good %= MOD;
			good += odd.getSum(max(MOD - a- shift, 0), MOD - 1 - shift);
			good %= MOD;
			good += odd.getSum(2*MOD - a - shift, MOD - 1);
			good %= MOD;
		}else{
			good += odd.getSum(0, MOD - a - 1 - shift);
			good %= MOD;
			good += odd.getSum(MOD - shift, MOD - 1);
			good %= MOD;
			good += even.getSum(max(MOD - a- shift, 0), MOD - 1 - shift);
			good %= MOD;
			good += even.getSum(2*MOD - a - shift, MOD - 1);
			good %= MOD;
		}
		shift = (shift + a) % MOD;
		if(shift == 0){
			even.add(0, good);
		}else if(shift % 2 == 0){
			odd.add(MOD - shift, good);
		}else{
			even.add(MOD - shift, good);
		}
		res = good;
	}
	cout<<res<<"\n";
}